Driving fluid from tank to piping system
Driving fluid from tank to piping system
(OP)
I have tried a number of equations and keep getting drastically different results.
With liquid water (say 15C) in a tank connected to a system open to atmosphere with 100 feet of head via an 8 foot section of 2" pipe, if the tank is pressurized with air in order to drive the tank water into the system, such that the air space is regulated to 5 PSIG above the static head pressure at the bottom of the system, what would the flow rate through the 2" pipe be? The tank discharge is level with the bottom of the system and there are 10 feet of liquid above the tank discharge in the tank. Once I figure out a satisfactory solution to this I would like to run it for a 3/4" pipe as well.
Just scratch on the envelope, I tried using Hazen-Williams assuming that the delta P is approx 10 PSIG (10 ft water plus the pressurized surface), a C of 120, and got 371 gpm.
That is,
10 psig / 8 ft = 4.52 * Q^1.85 / (120^1.85 * 2^4.87), solve for Q.
Dropping to a 3/4" pipe resulted in a 28 gpm result.
Is this on the right track?
Photo attached to post.
With liquid water (say 15C) in a tank connected to a system open to atmosphere with 100 feet of head via an 8 foot section of 2" pipe, if the tank is pressurized with air in order to drive the tank water into the system, such that the air space is regulated to 5 PSIG above the static head pressure at the bottom of the system, what would the flow rate through the 2" pipe be? The tank discharge is level with the bottom of the system and there are 10 feet of liquid above the tank discharge in the tank. Once I figure out a satisfactory solution to this I would like to run it for a 3/4" pipe as well.
Just scratch on the envelope, I tried using Hazen-Williams assuming that the delta P is approx 10 PSIG (10 ft water plus the pressurized surface), a C of 120, and got 371 gpm.
That is,
10 psig / 8 ft = 4.52 * Q^1.85 / (120^1.85 * 2^4.87), solve for Q.
Dropping to a 3/4" pipe resulted in a 28 gpm result.
Is this on the right track?
Photo attached to post.





RE: Driving fluid from tank to piping system
RE: Driving fluid from tank to piping system
RE: Driving fluid from tank to piping system
I did have a mislabel on the original drawing but it isn't the way you marked it up. For the sake of this initial go at the problem (calculate time required for the job of pushing a tankerful of new fluid into the existing system), I was told they would keep the air pressure on the tanker at approximately 5 psig over the static head pressure of the system into which they are pumping into which would be the 100 ft of head open to atmospheric pressure. The 10 ft static head in the tank will decrease as the liquid level there is pumped out but I want to look at the initial condition only right now. I marked the drawing correctly now and re-attached.
RE: Driving fluid from tank to piping system
P1 = 100 ft. of water = 43.3 psig
P2 = P1 + 5 psig ---> P1 = 48.3 psig
P at pipe exit = 48.3 + 10/2.31 = 52.6 psig
dP = 52.6 - 43.3 = 9.3 psi
I got 250 gpm for 2" Sch. 40 and 29 gpm for 3/4" Sch. 40.
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Driving fluid from tank to piping system
RE: Driving fluid from tank to piping system
Just be aware that these sorts of calculations are very sensitive to the ID that you use. So if any of the piping is in fact a hose or other type of 2" pipe then the ID might be quite different. Also whether the bore changes at any valves or connectors. I'm not surprised at the difference in flow between those two different pipes.
Given that the pressure P2 is constant, but the height changes, then as you say the flow will change and reduce as time goes on, so you're in a dynamic situation.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Driving fluid from tank to piping system
RE: Driving fluid from tank to piping system
RE: Driving fluid from tank to piping system
My handy dandy spreadsheet uses Darcy–Weisbach equation and methodology.
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Driving fluid from tank to piping system
Can you lay out the equations for those 3 pieces for me?
RE: Driving fluid from tank to piping system
It's a trial error process. You adjust the flow rate until it matches the given pressure drop
RE: Driving fluid from tank to piping system
See attached. I characterized the 8' long 2" Sch. 40 pipe with an entrance and exit loss. Then, entered the properties of water. Then I kept entering flow rates until pressure drop was about 9.3 psi. It took about a minute.
Good luck,
Latexman
To a ChE, the glass is always full - 1/2 air and 1/2 water.
RE: Driving fluid from tank to piping system
The exit loss from the tank is approximately the same as an orifice loss:
http://www.tlv.com/global/TI/calculator/water-flow...
Pipeline headloss can also be approximated:
http://irrigation.wsu.edu/Content/Calculators/Gene...
RE: Driving fluid from tank to piping system
Based on the last diagram posted, we have
Static head diff = 90ft = 27.3m of water = 38.8psi
Vapor space diff = 0-5 = -5psi
Net differential = 38.8 - 5 = 33.8psi, while you've used 9.3psi ?
RE: Driving fluid from tank to piping system
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Driving fluid from tank to piping system